In a prior art flasher device as illustrated in FIG. 1, turn signals or direction indicating lamps provided on a vehicle are controlled. This flasher device is disclosed in Japanese patent publication No. 57-50690 (50690/1982). In this device, there are provided pairs of left and right direction indicating lamps or turn signals lL, lR. These lamps lL, lR are alternatively selected by actuation of a flasher starting switch 2. The flasher starting switch 2 is provided with an intermediate position which provides a non selected condition. The stationary contacts 2a, 2b of the starting switch 2 are connected to the direction indicating lamps lL and lR. A movable contact 2m of the starting switch 2 is supplied a supply voltage V.sub.B via a current detecting resistor 3 and a relay switch 4. The relay switch 4 is turned on when a relay coil 5 is energized. One end of the relay coil 5 is supplied the supply voltage V.sub.B and the other end of the relay coil 5 is selectively grounded via a collector and an emitter of a switching transistor 6.
The base of the switching transistor 6 is connected an oscillator 8 via a resistor 7. The voltage developed across the current detecting resistor 3 is supplied to a discriminator circuit 9. In the preferred embodiment the discriminator circuit is formed of a comparator. The discriminator circuit 9 determines whether there has been a disconnection or failure of a filament of one of the pairs of direction indicating lamps lL and lR from the voltage V.sub.B supplied the lamps lL, lR via the current detecting resistor 3. The output of this discrimination circuit 9 is supplied to the oscillator 8. The oscillator 8 is constructed so that when the flasher starting switch 2 is operated to turn on one of the pairs of lamps lL, lR, the oscillating actuation is started, for example, by a switch associated with the starting switch 2 so as to generate an oscillating signal which is provided to the transistor 6. The oscillator circuit is responsive to the output of the discrimination circuit 9 so that the oscillation frequency varies according to the output of the discriminator circuit 9.
In such a structure, when the starting switch 2 is operated by movement from the intermediate position to one stationary contact, the oscillator 8 begins oscillation and the oscillating signal is supplied to the base of the transistor 6 via the resistor 7. As a result, the transistor 6 starts its ON/OFF actuation and the voltage V is applied intermittently to the relay coil 5 with the oscillating frequency of the oscillator 8. Accordingly, since the relay switch 4 turns on and off, the electric current due to the voltage V.sub.B flows intermittently to ground through the resistor 3, the relay switch 4, the starting switch 2 and the selected pair of direction indicating lamps lL or lR thereby allowing the direction indicating lamps lL or lR to flash. During this time, the current which flows in the selected pair of direction indicating lamps lL or lR is detected by the resistor 3. The output of the discriminator circuit 9 inverts from a low level output to a high level output when the voltage across the resistor 3 drops below a required voltage when the transistor 6 turns on. The oscillator 8 changes its oscillating frequency according to the high level output. For example, if the filament of one lamp of the selected pair is broken when the two direction indicating lamps lL are flashing, since the current which flows through the series circuit consisting of the resistor 3, the relay switch 4, the starting switch 2 and the other direction indicating lamp lL reduces to about 1/2 the normal current, the voltage across the resistor 3 falls below the required voltage causing the output of the discriminator circuit 9 to go high and thus raising the oscillating frequency of the oscillator 8. Accordingly, the flashing becomes faster at the other direction indicating lamp lL whereby the vehicle driver may discover the breakdown of the filament of the one direction indicating lamp lL.
In such a flasher device, it is necessary to provide a current detecting resistor in a current path of the direction indicating lamp. Accordingly, the resistance of the current detecting resistance lowers the voltage across the direction indicating lamps, thus lowering the luminous intensity of the direction indicating lamps and reducing power consumption efficiency.
A flasher device is disclosed in Japanese patent laid open No. 55-140622 (No. 140622/1980) which overcomes the disadvantages of the FIG. 1 Prior Art. This laid open application discloses a device in which a resistor is provided in parallel with a relay switch and an electric current is supplied to direction indicating lamps through the resistor during the turned off period of the direction indicating lamps whereby a breakdown of the direction indicating lamp is detected from a terminal voltage of the direction indicating lamp immediately after turning off the relay switch. However, since it is necessary to always supply some current to the direction indicating lamp, electric power is very wastefully consumed.
Such a flashing device carried on a vehicle, usually is provided with an automatic cancelling function which automatically cancels flashing of a direction indicating lamp, for example, according to a turning angle of a handle, a travelling distance or the like. This is convenient, since in such a device it is sufficient to operate a flasher switch only when starting the flashing of the direction indicating lamp. It is desirable for the operation of the automatic cancelling function to be announced to the vehicle operator when the vehicle is travelling and where the flashing of the direction indicating lamp has been automatically cancelled.
As a device of this kind, Japanese laid open patent No. 50-139689 (No. 139689/1975) discloses a device which generates flashing actuation sounds from a speaker or the like according to a flashing period during the flashing of a lamp. However, in such a communication, the sound is always generated during the flashing of the lamp and is therefore offensive to the ear and increases the consumption of electric power.